The present invention relates to a scanning mechanism for a vehicle-mounted radar apparatus.
As a conventional vehicle-mounted radar apparatus, an apparatus such as the one shown in FIG. 6 is known.
In the drawing, an antenna transmission/reception section 31 is comprised of an antenna unit 32, a coupler 33, a voltage controlled oscillator 34, a frequency conversion unit 35, and a gain control unit 36. Further, a signal processing section 37 is comprised of a modulated-signal control unit 38, a frequency analysis unit 39, and an arithmetic-operation control unit 40. Reference numeral 41 denotes a mechanical driving section.
In the vehicle-mounted radar apparatus configured as described above, the modulated-signal control unit 38 supplies a modulation signal to the voltage controlled oscillator 34 to allow the voltage controlled oscillator 34 to generate relatively high frequency radio waves subjected to linear frequency modulation. The relatively high frequency radio waves subjected to linear frequency modulation and outputted from the voltage controlled oscillator 34 are radiated to space from the antenna unit 32 via the coupler 33. Meanwhile, received radio waves from an object which reflects transmitted radio waves are received by the antenna unit 32 and are supplied to the frequency conversion unit 35.
In the frequency conversion unit 35, part of the transmitted radio waves from the coupler 33 and the received radio waves from the antenna unit 32 are mixed, and a relatively low frequency signal is generated. An amount of transition of a frequency based on the time lag of radio waves corresponding to the distance to the object and an amount of transition of a Doppler frequency based on the moving velocity in a case where the object is moving are added to the frequency of the received radio waves. Accordingly, information such as the relative distance to the object and the relative velocity are multiplexed with the relatively low frequency signal generated by the frequency conversion unit 35. The power of this multiplexed signal is set by the gain control unit 36 in such a manner as to assume an appropriate magnitude for each scanning of the transmitted radio waves and the transmitted radio waves by the mechanical driving section 41, and the arithmetic-operation control unit 40 computes the relative distance, the relative velocity, and the like with respect to the frequency data from the frequency analysis unit 39.
Next, a description will be given of the above-described mechanical driving section 41.
As a device for effecting scanning to receive radio waves reflected from an object located in an arbitrary direction, a device which uses a quadric link mechanism such as the one shown in FIG. 7 is known.
In the drawing, the antenna transmission/reception section 31 is rotatably supported by a swinging shaft 42. A connecting pin 43 is formed integrally with the transmission/reception section 31, and one end of a connecting link 44 is connected to the connecting pin 43 via a bearing, while the other end of the connecting link 44 is similarly connected rotatably to an eccentric pin 45 via a bearing. A disk 47 is attached to a rotating shaft 46.
Next, a description will be given of a scanning mechanism.
As the rotating shaft 46 is rotated at an equal velocity by, for example, a motor (not shown) and an appropriate speed-reducing mechanism (not shown), the eccentric pin 45 undergoes rotary motion on a circle r indicated by the dotted-dash line in FIG. 7. Since one end of the connecting link 44 is rotatably connected to the eccentric pin 45 via the bearing, and the other end thereof is similarly connected via the bearing to the connecting pin 43 provided on the antenna transmission/reception section 31, the antenna transmission/reception section 31 undergoes swinging motion about the swinging shaft 42. That is, a quadric link mechanism having as its nodal points the swinging shaft 42, the connecting pin 43, the eccentric pin 45, and the rotating shaft 46 is mechanically formed, whereby the rotary motion of the rotating shaft 46 is converted to the swinging motion of the connecting pin 43. Since the connecting pin 43 is formed integrally with the antenna transmission/reception section 31, the antenna transmission/reception section 31 undergoes swinging motion about the swinging shaft 42 so as to continuously change the direction of transmission and reception of radio waves, thereby effecting scanning.
At this time, the change over time of a swinging angle .theta. of the antenna transmission/reception section 31 assumes a substantially sinusoidal function, as shown in FIG. 8.
Since the conventional vehicle-mounted radar apparatus is configured as described above, the scanning velocity is high in the vicinity of the frontal direction for which particularly detailed angular information is required, as shown in FIG. 8. Therefore, the angle measuring accuracy becomes relatively low, so that there has been a problem in that the amount of information obtainable for the frontal direction becomes small.
In addition, although it is conceivable to overcome the above-described problem by adopting a cam mechanism as the scanning mechanism so as to obtain equal velocity scanning, in the case of an electromagnetic radar, the mass of the antenna transmission/reception section for effecting scanning is liable to become large. Hence, there is a drawback in that a problem occurs, such as the occurrence of a jump at the cam surface and a decline in the durability.